1. Field of the Invention
The invention relates to an apparatus and a method for processing plastic waste which is contaminated with, for example, food, paper, and metal, into densified blocks in order to reduce the volume of such waste and the corresponding storage space associated therewith. More particularly, the inventive apparatus and method are directed toward processing plastic waste to produce a plastic slug that is suitable for long term sanitary storage.
2. Description of the Related Art
Navy ships generate plastic waste at a rate of approximately 0.1-0.2 pounds per man per day (0.045-0.09 Kg per man per day). This plastic waste is of very low density, approximately 1.4 pounds per cubic foot (22.4 Kg per cubic meter) and about 60% of this waste is heavily contaminated with food. Historically, all of this plastic waste has been discharged at sea, but this method of disposal has been ended due to its negative environmental impact.
The types of plastic waste typically encountered on ships are reflected in Table 1. Thus, any method or apparatus which is used to process such plastic must be capable of operating when the plastic waste includes a variety of different plastics which can also be contaminated with food, oil, water, metal and other non-plastics.
TABLE 1 ______________________________________ SOURCES OF SHIPBOARD PLASTIC WASTE TYPE OF PLASTIC SOURCE ______________________________________ SOFT CELLOPHANE FOOD AND CLOTH- ING PACKAGING POLYETHYLENE- PACKAGING, TRASH POLYSTYRENE BAGS, FILM PACKAGING, FILMS HARD NYLON MOLDED PARTS POLYETHYLENE CONTAINERS TEREPHTHALATE(PET) POLYETHYLENE CONTAINERS, MOLDED PARTS POLYSTYRENE CONTAINERS, MOLDED PARTS POLYVINYL CHLORIDE PIPING, HOUSINGS FOAM POLYETHYLENE PACKAGING POLYSTYRENE PACKAGING, PADS POLYURETHANE PACKAGING, FOAM CUSHIONS ______________________________________
Existing technologies for processing and handling plastic waste include containment, heat, pressure, and screw type plastic recycling extruders. However, each of these existing technologies has disadvantages associated therewith and all are suited to an open factory environment versus a confined environment such as on board a ship. In containment, the plastic waste is placed in a heat shrinkable plastic bag and the ends of the bag are sealed with a heat gun. This results in the sanitary containment of the plastic waste, but does not reduce the volume of the plastic waste.
Pressure techniques such as that provided by a trash compactor can reduce the volume of waste. However, very high pressures in the order of 5,000 to 10,000 psi are required to produce an acceptable density level. Moreover, when the compressed waste (slugs) are handled, they tend to flake apart creating an unsanitary condition. In addition, based on testing conducted by applicants, it was determined that no amount of pressure could maintain the slugs in their compressed shape for more than five minutes. That is, due to the elastic memory of the plastic waste only a moderate permanent reduction in volume occurs. In order to overcome this problem, the compacted plastic waste can be banded immediately after compression. However, this requires a subsequent labor intensive step. The pressure compaction method is also deficient in that no sterilization of the waste stream is provided. That is, while the contaminated mixed plastic waste is compacted to have a reduced volume, it is not in a sanitary inert form such that it can be stored for a long period of time without creating a health hazard. Thus, the compressed contaminated plastic must be disposed of in a short period of time.
Heating the plastic waste and allowing it to cool can increase the density (reduce the volume) of the plastic waste. However, extremely high temperatures of approximately 450.degree. F. are required to produce any significant reduction in the volume of the plastic waste. Furthermore, even at 450.degree. F. the density of the heat-formed slug is still less than that produced by the compaction technique at 10,000 psi. Moreover, there is a limit as to how high a temperature can be applied in order to prevent the creation of unpleasant or noxious fumes that can be generated if oils and other materials begin to burn.
Plastic screw type extruding systems, such as those used in the recycled plastics industry, require the plastic waste to be carefully sorted, washed, and dried prior to being processed. These processes are very labor, time and space intensive. In addition, plastic extruding systems have not been used for processing plastic heavily contaminated with food, oil and non-plastic components. Oil, either from machinery spaces or food oil containers, would likely reduce the friction within the screw type extruder. Such friction is, however, essential for the melting that takes place within the extruding system, and therefore, any reduction of friction would form a slug of unknown properties. Furthermore, any metal contamination of the plastic waste would likely damage the extruding system. That is, the screw type extruder requires very tight tolerances. A piece of metal, such as a knife, in the plastic waste being processed would severely damage a screw extruder.
Another problem with extruding systems occurs if the processed plastic is wet. The wet plastic can cause a vapor lock such that the plastic stream exiting the extruder would be foam or would have steam explosions.
In view of the above, it is readily apparent that the screw type extruding system requires the waste introduced therein to be sorted and cleaned prior to entering the system in order to help prevent the above-mentioned problems from occurring. The sorting operation could be done manually or accomplished by using metal detectors. In addition, a shredder can be added to the extruder system to shred the incoming waste such that contaminates are finely ground so that they no longer threaten damaging the screw extruder. In any event, the use of an extruding system requires extensive and costly preparation of the incoming waste prior to its subsequent processing.
Additional equipment used for municipal waste streams such as balers, are typically very large and provide no means of sterilizing the waste stream without some type of covering or strapping.
It is readily apparent that the prior art lacks a method and apparatus which are simple in design and which allow for contaminated mixed plastic waste to be processed into a sanitary inert form such that it can be stored for a long time without creating a health hazard.